Background: Diabetic macular edema (DME) is a serious complication of diabetic retinopathy (DR).Recent studies have shown that inflammation is closely associated with the development of DME, and peripheral blood inflammatory markers [white blood cell (WBC) count and its subtypes] are relatively simple and easy to detect. Here, we investigated the relationship between peripheral blood inflammatory markers and macular edema in patients with severe DR (including both severe non-proliferative DR and proliferative DR).Methods: A total of 42 patients with severe DR were included in this study and divided into two groups: a severe DR with DME group (DME group, n=18) and a severe DR without DME group (non-DME group, n=24). Ophthalmologic findings and hematologic results were retrospectively retrieved from hospitalization records and databases.Results: The neutrophil percentage was significantly higher in the DME group (62.52%±8.21%) than in the non-DME group (57.30%±8.17%) (P<0.05); in contrast, the lymphocyte percentage was significantly lower in the DME group (28.09%±7.45%) than in the non-DME group (33.54%±7.29%) (P<0.05). Logistic regression analysis showed a significant correlation between lymphocyte percentage and DME [odds ratio (OR) =0.654, 95% CI: 0.436-0.851; P=0.011].Conclusions: Lymphocyte percentage can be used as an inflammatory marker for the development of DME in patients with severe DR.